A few years back, when I started having the intercostal neuralgia, I was put on Fentanyl, as many opiate drugs make me sick. This is a multi-tiered question: If you have been on Fentanyl, can you sleep on it? I can sometimes, but rarely. I feel doped and it messes with my brain when I lay down and the more I lay down, don't move, etc...the more doped I become on it. Also, are there times you can take a medicine and it's okay for you and other times it's not? For me, I can take Fentanyl and have no mood swings and other times it makes me into a raving you know what. I feel crazy on it. Chemistry is constantly changing and that is the only thing I can figure out. Sometimes I do great, other times...not so much. Still missing Darvocet. Best drug ever.